'Life and death'

"It's human milk that gets their gut primed, it's human milk that fights any infections that they can get. It constantly changes to fight all the new infections that they're liable to have."

She added that in some cases, donated milk could mean "the difference between life and death".

The Fermanagh facility, run by the Western Health and Social Care Trust, opened 17 years ago and serves every neonatal unit on the island of Ireland.

Last year, it provided milk for more than 900 babies, one of its busiest periods ever, with an increase of 50 babies on the year before.

'Nutritional content'

Many of the recipients are increasingly premature and extremely vulnerable.

"What we're noticing is that we're helping more of the very tiny babies," Ms McCrea said.

"We seem to be helping more of these 24, 25-week olds that are born.

"The other thing is that there's been a huge increase in the number of twins, triplets and quads that we've helped in the last year, and they take quite a lot of milk, obviously, because mums find it harder to produce enough milk for their babies."

The manager thinks the increase in demand is due to a greater understanding of the benefits of breast milk.

She said neonatal units were also looking for specific donations of milk for very early babies because "it's higher calorie and has better nutritional content for premature babies, for optimal growth".

Despite recent donor recruitment, only one third of the milk bank's freezers are currently full, which equates to about two week's of supply.

'Temporary crisis'

The health trust has described this as an "exceptional shortage" and has appealed for donors to act quickly, particularly mothers who already have breast milk stored in their own freezer.

The milk bank's manager said it is not the first time stocks have run low and they usually get a very good response to appeals.

"I'm just hoping this is just a temporary crisis," said Ms McCrea.

"Normally when we put out an appeal, mummies out there get their breast pumps out and they help us and the stocks just build up again."

However, the bank need at least three litres per volunteer to make it cost effective, as all donations have to be screened for disease.

"All our donors have to be blood-tested for HIV; hepatitis B and C; HTLV 1 and 2 [Human T-cell lymphotropic virus] and syphilis.

"So, it helps keep the costs down because it's the blood tests that actually do cost quite a lot in this process," Ms McCrea said.

"We have to make sure that our milk is well screened, so the best quality, the safest milk, goes to our smallest, tiniest babies."

An interview with Ann McCrea will be broadcast on the BBC's Good Morning Ulster programme after 07:30 GMT on Monday.